1. Field of the Invention
This invention relates to poly(glycidyl nitrate) plasticizers and their use in energetic formulations.
2. Description of the Prior Art
Poly(glycidyl nitrate) (PGN) is an energetic polymer structurally related to the well known glycidyl azide polymer (GAP). Although they are structurally similar, PGN and GAP are synthesized by different routes. GAP is synthesized by first polymerizing epichlorohydrin (ECH) (e.g., glycidyl chloride) to poly(epichlorohydrin) (PECH), then the PECH is converted to GAP by reaction with sodium azide in dimethylsulfoxide. PGN, on the other hand, is synthesized by first converting ECH to glycidyl nitrate (GN) by a two-step procedure; then the GN is polymerized to PGN. Because of the cheaper reagents used in the synthesis and the simpler synthetic scheme employed, PGN would be potentially much cheaper to produce than GAP.
Although most recent work on energetic polymers has centered on GAP and various poly(oxetanes), PGN was in fact the first energetic prepolymer investigated. The initial work on PGN was done by Thelen et al in the 1950's at the Naval Ordnance Test Station (NOTS, now NWC). They studied the polymerization of glycidyl nitrate by a variety of Lewis acid catalysts with most of the work centering on the use of stannic chloride (SnCl.sub.4) as the catalyst. No propellants were prepared by the NOTS workers and they noted that one drawback to their synthesis was the laborious purification procedure.
PGN and PGN propellants were next examined at the Jet Propulsion Laboratory (JPL). The JPL workers found that PGN made using boron trifluoride etherate was low in both functionality (i.e., 2) and molecular weight (M.sub.n =1500) and therefore polyurethane propellants made from this PGN had poor mechanical properties. Similar observations were made by other workers. In summary, it has long been recognized that PGN would be an excellent energetic polymer but until now a method of synthesis could not be found that would produce nearly difunctional material with acceptable hydroxyl equivalent weights.
The synthesis is described in allowed U.S. Pat. No. 5,120,827 hereby incorporated by reference, in toto.